Process for the extraction of glyceride oils by selective solvents

ABSTRACT

Process for the recovery from edible oils containing at least 50% linoleic acid combined as glycerides, of a fraction enriched in combined linoleic acid, in which the oil is contacted with an organic polar solvent immiscible therewith, the liquid phases formed being separated and the enriched fraction recovered from the polar solvent. Dialkyl lower amides are preferred polar solvents and sunflower, safflower and cottonseed oil are preferred oils.

United States Patent [1 1 Parsons July 1, 1975 PROCESS FOR THEEXTRACTION 0F 2,573,900 11/1951 Freeman 260/4285 3,376,326 4/1968 Artmanet al 260/410] GLYCERIDE OILS BY SELECTIVE SOLVENTS fXT/PAC'T/VE COLUMNSPrimary ExaminerDonald G. Daus Assistant ExaminerDiana G. RiversAttorney, Agent, or FirmJames J. Farrell; Melvin l-l. Kurtz Arnold Grant[5 7] ABSTRACT Process for the recovery from edible oils containing atleast 50% linoleic acid combined as glycerides, of a fraction enrichedin combined linoleic acid, in which the oil is contacted with an organicpolar solvent immiscible therewith, the liquid phases formed beingseparated and the enriched fraction recovered from the polar solvent.Dialkyl lower amides are preferred polar solvents and sunflower,safflower and cottonseed oil are preferred oils.

11 Claims, 1 Drawing Figure PROCESS FOR THE EXTRACTION OF GLYCERIDE OILSBY SELECTIVE SOLVENTS BACKGROUND OF THE INVENTION l. Field of theInvention This invention relates to the extraction of glyceride .oils byselective solvents and particularly to the application of such treatmentto sunflower or similar oils for the purpose of enhancing their contentof combined polyunsaturated fatty acids. Sunflower and safflower oilsare widely used as ingredients in the manufacture of margarine and otheremulsion food spreads. They alsofind wide application for other edibleproducts, for example in frying oils.

lt'is widely accepted to be beneficial to include in the diet a fatintake containing a high proportion in its combined form of linoleicacid, a so-called essential fatty acid. This contains two ethylenicallyunsaturated bonds, whereas linolenic acid contains three double bonds,and is less desirable nutritionally and more susceptible todeterioration in storage. Sunflower oil often contains 60-70% linoleicacid, while safflower oil usually contains 7080%. The remaining fattyacid content of these oils is shared principally between C and Csaturated and monounsaturated fatty acids. Such oils should bedistinguished from drying oils which are characterized by even moreunsaturation, with a high content of linolenic acid and otherunsaturated fatty acids in combined form which contain three or moredouble bonds, which oils are often inedible.

The invention is based upon the observation that the glycerides of thehighly unsaturated fatty acids commonly found in natural fats, i.e.linoleic and linolenic,

are more soluble in polar solvents than those of the principal saturatedand mono-unsaturated acids commonly occurring with them, i.e. of 16 and18 carbon atoms in chain length. Preferably those oils are selectedwhose linolenic acid content is low, since this is a less desirablecomponent, prone to atmospheric oxidation with the development ofoff-flavours and less desirable nutritionally. In addition to sunflowerand safflower oils, maize and cottonseed oils are particularlypreferred. soyabean oil less so but nevertheless within the scope of theinvention.

2. The Prior Art Liquid-liquid extraction has been extensively developedby the petroleum industry for the separation of saturated andunsaturated, especially aromatic hydrocarbons. Sulphur dioxide has beenused e.g. in the Edeleanu process since about 1909 and furfural since1935. Phenols, at first used in batchwise extractions were later used inconjuction with propane. Dimethylformamide was first suggested in 1942but was not then given serious consideration.

All these processes have been considered for refining lubricating oilsor for removing impurities from fuel oils. With the development ofcatalytic re-forming more sophisticated techniques were necessary toremove aromatics in a useable form. Multi-stage contactors wereintroduced with light hydrocarbon for the stripping section. New polarsolvents included diethylene glycol in the Udex process (British Pat.No. 739,200 Dow), sulpholane (British Pat. No. 980,973 Shell), N'methylpyrrolidone in the Arosolvan and Lurgi processes (Belgian Pat. No.613,126), dimethylformamide (British Pat. No. l,l04,5 l 3),N-formylmorpholine and tetraethylene glycol. The application ofliquid-liquid extraction techniques to the treatment of edible fats andoils of the glyceride type has also been the subject of extensiveinvestigation in the art. In US. Pat. No. 2,200,390 the extraction ofboth edible and non-edible ie drying glyceride oils with a wide range offuran compounds is described. Freeman also examined a much wider rangeof solvents in US. Pat. No. 2,200,391, including the unsubstituted alkylamides from formamide to butyramide.

DETAILED DESCRIPTION OF THE INVENTION The present invention proposes toincrease the combined polyunsaturated fatty acid content of edible oils,particularly in glycerides of linoleic acid, of oils generally whosecombined linoleic acid content is at least 50% by weight, by a processcomprising contacting the oil with a suitable solvent system comprisingan N- substituted amide solvent at a temperature at which two liquidphases are formed, one consisting of a fraction of the oil rich incombined linoleic acid which is dissolved in the polar solvent, and theother a lean fraction comprising the residual oil, separating the twofractions and removing the polar solvent from the rich fraction torecover an oil fraction rich in combined linoleic acid.

The invention is based upon the observation that the glycerides of thehighly unsaturated fatty acids commonly found in natural fats, ielinoleic and linolenic, are more soluble in polar solvents than those ofthe principal saturated and mono-unsaturated acids commonly occurringwith them, ie of 16 and 18 carbon atoms in chain length. Preferablythose oils are selected whose linolenic acid content is low, since thisis a less desirable component, prone to atmospheric oxidation with thedevelopment of off-flavours and less desirable nutritionally. Inaddition to sunflower and safflower oils, maize and cottonseed oils areparticularly preferred, soyabean oil less so but nevertheless within thescope of the invention.

By means of the invention a fat fraction may be obtained suitable foruse in foods in which sunflower and safflower oils are conventionallyused but which contains as much as 10 or 20% additional polyunsaturatedfatty acid in combined form, or even more. Suitable products includeedible oils for salad frying oils, salad creams, margarine and low fatemulsion-type spreads and shortening.

Organic polar solvents suitable for use in the invention include amidescontaining two lower alkyl groups, preferably each containing up to 4carbon atoms, attached to the nitrogen atom of the amide group,particularly N-lower alkyl pyrrolidones, particularly the methylderivative and dimethyl formamide. It may be necessary with the formersolvent to realise an adequate degree of immiscibility by the additionthereto of a minor amount of water or a lower alkylene diol having up to4 carbon atoms, eg ethylene glycol, generally less than 15% of thelatter and less than 2% water, according to the extraction temperature.

Preferably the oil is itself dissolved in a non-polar solvent with whichthe extracting solvent is immiscible, thereby increasing the densitydifferences between the phases and thus facilitating their separationfrom one another and the selectivity extraction for polar relative tonon-polar glycerides, ie for polyunsaturated to less highly unsaturatedglycerides. Suitable oil solvents include aliphatic hydrocarbons whichcan conveniently be handled in liquid form, ie saturated aliphatichydrocarbons from 3 to carbon atoms in chain length, although the upperlimit is not critical. Suitable hydrocarbon solvents include propane,butane, hexane and other light fractions, particularly a heptanefraction with a boiling range (95%) 96-98C petroleum. These hydrocarbonsolvents are essentially non-polar and are customarily adopted in theextraction of the oils with which the invention is concerned from theirplant seeds following the conventional dressing operation, to increasethe yield of oil.

The extraction using a polar solvent may be carried out continuously orbatchwise. A particularly effective method of carrying out continuousextraction is by the method of countercurrent liquid-liquid extraction.In this method the immiscible liquids flow in opposite directionsthrough a column or columns fitted internally with means providingmaximum contact between the two. The columns may be packed with randompacking, e.g. Raschig rings, or fitted with spaced plates in a mannerwell known in the art for the purpose of affording maximum liquid-liquidcontact. Alternative mixer/- settler apparatus may be used instead.

In use, the polar and non-polar solvents or reflux oil if no non-polarsolvent is used are fed into opposite ends of the column and the oil tobe extracted from an intermediate position.

The choice of solvents is determined among other things by therequirement to provide substantial immiscibility and they should also beinert both towards the oil being extracted and to one another where twosolvent systems are utilised. Their properties in this respect may bemodified according to the temperature at which they are used. Organicpolar solvents selected for use in the invention must be substantiallyimmiscible with the oil and/or its solution in a non-polar solvent. Thedegree of immiscibility may however be materially affected by thetemperature at which the extraction is carried out. Further, byappropriate choice of temperature the degree of selectivity exercised inthe extraction process according to the invention, between unsaturatedglycerides and others in the oil being extracted may be substantiallymodified by temperature change.

Where a non-polar solvent is used it should not be in excess of theamount of polar solvent used to extract the polyunsaturated fatty acidglycerides; for example, 4 to 40 parts of polar solvent per part ofhydrocarbon, or other non-polar solvent, and in particular from 10 to 30parts of polar solvent per part has been found satisfactory. Therelative amounts of the immiscible liquids should be selected bearing inmind the partition coefficients determining the distribution between thetwo solutes concerned, ie the glycerides of different degrees ofunsaturation. In order to obtain the correct rates the degree ofimmiscibility should also be taken into account and preliminaryexperiments may be necessary to ascertain the best proportions to adopt.However, a linoleate partition coefficient greater than 50 requires anexcess of polar solvent so great as to be uneconomic and an upper limitof about is generally imposed.

The recovery of glycerides from the polar solvent used in the extractionis preferably effected by diluting with water and extracting withnon-polar solvent followed if necessary by distillation to recover thesolvents in a form suitable for recycling.

Preferably the extraction procedure is carried out at temperaturesbetween 20 and +50C. The lower temperatures may be necessary where avolatile hydrocarbon is used as a solvent, but in general preferably theextraction is carried out at moderately elevated temperatures within theabove range. The process may be carried out under atmospheric orsuperatmospheric pressures, the latter being necessary to avoid the useof excessively low temperatures where highly volatile solvents are used.

The oils are preferably bleached and neutralised before treatment in theprocess of the invention.

The recovered enriched glycerides may be used for the manufacture ofmargarine and other edible emulsion spreads where a high content ofpolyunsaturated fatty acids in combined form is required. A minorproportion of semi-solid or hard fat, eg lauric fats and particularlycoconut oil, palm oil or hardened fats, for example hardened soyabeanoil and cottonseed oil or stearine fractions thereof, are preferablyincluded in the fat composition for these purposes.

Apparatus suitable for carrying out a continuous extraction process forthe separation of saturated and unsaturated fractions (these being usedas comparative terms) of a glyceride oil in accordance with theinvention comprises a pair of packed liquid-liquid extraction columnsarranged in series and a fractionation column connected to the base ofthe second column for recovering the polar solvent, in a sufficientlypurified form to be recycled to the top of the first column.

A recovery unit comprising for example a multiple effect evaporator,separator and distillation equipment is provided for each extractioncolumn, to remove any hydrocarbon solvent from the separated oilfractions which are collected in the effluent from the tops of theextraction columns.

In use, the oil, for example sunflower oil, is admitted into the firstcolumn. Where a non-polar solvent is used, for example a lighthydrocarbon solvent, this is admitted to the base of both columnscountercurrent to the heavy polar solvent admitted to the top. Eachsolvent may be previously saturated with the other. A small proportionof water may be admitted with the base effluent passed from the firstcolumn to the top of the second column to facilitate extraction therein.

The saturated and unsaturated fractions of the sunflower oil aredistributed between the hydrocarbon and polar solvents in the firstcolumn. Effluent from the tops of the columns are treated in therecovery units to remove any light solvent, consisting larely of thehydrocarbon, for example by evaporation. Polar solvent may be separated,for example by water washing, from the more saturated fraction of theoil.

The more unsaturated fraction, extracted from the oil in the firstcolumn by the polar solvent, is reextracted therefrom in the secondcolumn by the hydrocarbon solvent if this is used, and similarlyrecovered in the second recovery unit, in which the effluent from thetop of the second column is treated.

DESCRIPTION OF THE DRAWING Referring now to the drawing, an oil feedsupply, for example of sunflower oil, enters the system via line 11 andis introduced into extractive distillation column 10 between its ends, apolar solvent being introduced above and a non-polar solvent below thepoint of entry of the oil via lines 12 and 13, preferably at entrypoints adjacent the ends of the column, which may be packed randomly orotherwise furnished with plates, trays or the like to promote intimatecontact in the column between the liquids.

From column two liquid streams are withdrawn, the lighter stream viaupper line 14, conveying a lean fraction of the oil, dissolved in thenon-polar solvent to a recovery system comprising multiple-effectevaporahexane (3). On standing, the epiphase is less polar upper layer,was separated and weighed and the polar solvent in it extracted byrepeated water washing, carried out by shaking as before. The oilremaining was also weighed and the miscibility of solvent in the oillayer and quantity of oil extracted were calculated by difference.

Further particulars appear in Table I.

TABLE I Composition by weight Oil 7r linoleate Solvent extracted ln OilSolvent Tcmp.C Oil in hypo- Before After ln ratio phase Extract ExtractExtract.

(1) 27 2 l 19 66.3 64.6 70.7 45 2 l 40 66.3 65.4 67.8 (2) 20 20 l 6660.5 54.7 63.5 20 1O l 41 60.5 57.7 64.6 20 5 l 19 60.5 54.7 85.2 (3) 258 l 36 64.3 73.l 35 5 1 3l} 67.5 62.9 73.1 52 5 l 49 64.2 70.9

tor 30, and the heavier stream of a rich fraction of the oil in polarsolvent, via line to the upper second extraction column 20, togetherwith a minor proportion of water.

Into column 20, similarly equipped internally, a supply of non-polarsolvent is also admitted via line 21, countercurrent to the stream ofrich fraction, to strip this from the polar solvent. Duly stripped, thissolvent is discharged from the lower extremity of column 22 via line 22,into a solvent recovery column 50 through a feed point between the endsthereof. The column 50 isfitted with reflux condenser means 51, supplyand return lines therefor 52 and 53 and discharge line 54 via whichnon-polar solvent is delivered to storage means 60. Column heater 71 issimilarly furnished with corresponding lines 72, 73, and 74, the lattersupplying recovered polar solvent to storage means 70.

From the upper extremity of column the rich fraction, now dissolved innon-polar solvent, is delivered through line 23 to a recovery systemcomprising multiple-effect evaporator 40.

The evaporators 30 and 40 are correspondingly equipped with heatingmeans 31 and 41, delivery and return lines therefor 32, 33 and 42, 43and discharge lines 34, 44 from which the separated lean and rich oilfractions are collected.

The volatile products of the evaporators 30 and 40, consisting largelyof solvent, are delivered via lines 34, 44 and condensers 80, 90 toseparators 81, 91, from which separated non-polar solvent is dischargedto storage 60 via lines 82, 92 and polar solvent via lines 83, 93 tostorage 70.

EXAMPLE 1 Samples of sunflowerseed oil were thoroughly agitated inpredetermined weight ratios for 5 minutes at various temperatures withdimethylformamide l), a

mixture of 9 parts w/w N-methyl pyrrolidone per part 0 of ethyleneglycol (2) or 1,6-bispyrrolidon-2-yl-i- Although all three solvents wereeffective, a substantial proportion remained in the oil layer andincrease in temperature aggravated this tendency until the three phasesbecame completely miscible. Complete miscibility was similarly producedwhen the ethylene glycolzN-methyl pyrrolidone ratio was increased to1:19.

In a series of comparative tests, acetonitrile, tetraethylene glycol,N-methyl pyrrolidone with equal parts ethylene glycol and furfural with2% water, were all examined and all found to be inferior as polarsolvents, extracting less than 2% of the oil, with only slightsegregation of linoleic acid.

EXAMPLE 2 In this Example a series of tests on the solvents used inExample 1 in accordance with the invention was carried out as describedin that Example, using however heptane as a non-polar solvent to raisethe density difference between the phases and improve selectivity.

The non-polar phase was weighed and washed with water as before. Thewashed residue (epiphase) was weighed in order to determine themiscibility, the second solvent was removed by evaporation in order todetermine the quantity of oil remaining in the epiphase and to provide asample for fatty acid analysis. From the distribution of fatty acids,obtained by chromatographic analysis of the phases, a partitioncoefficient, calculated on the basis of the distribution of combinedfatty acids themselves, was then determined, representing theconcentration of linoleic acid as triglycerides in the epiphase dividedby that in the hypophase. The factor B in Table 2 is the ratio ofpartition coefficients for linoleic acid and the remaining acids andtherefore indicates the degree of enrichment, relative topolyunsaturated fatty acid content, effected by the extraction. Aminimum [3 value of 1.4 was regarded as providing effective separation.

Further particulars of the tests and results also appear in Table II.

TABLE [1 -Continued Components Linoleic Acid 1 Oil into 1.7! Content wt.'7! B hypophase Test Temp. Oil Solvent Heptane Oil Hypophase wt. 9:

C DMF DMF Dimcthfll'ormumidc NMPIH -O N-mcthyl pyrrolidone-titer (49:1

EXAMPLE 3 A continuous liquid-liquid extraction of sunflower oil usingdimethylformamide and heptane was carried out on sunflowerseed oil at20C in a 10-stage mixer settler of the Wall type (AERE/CElR 1730,Harwell 1955), in the modified form described by Ellis and Gibbon(Proceedings, Symposium Institute Chem. Eng. 24-26 April 1963). The oil,containing 65.4 wt linoleic acid was fed at a rate of 3 g/hr. to theepiphase leaving stage 5, while dimethylformamide and heptane, eachpreviously saturated with the other, were fed to stage 10 and stage 1 atrates of 225 and 8.7 g/hr.

Equilibrium was reached in 2 hours, when the composition of theeffluents became constant; the heavy solvent effluent contained 21% oilhaving a linoleic acid content of 84.7%, while the remainder of the oilin the light solvent contained 55.1% linoleic acid.

Upon raising the oil flow rate to 5.3 g/hr. the heavy solvent effluentwas found to contain 28.5% of the oil, with a linoleic acid content of81.9%, the remainder of the oil in the light solvent containing 56.8%linoleic acid.

Substantially higher oil rates were found to induce homogeneity betweenthe phases.

EXAMPLE 4 A continuous liquid-liquid extraction of sunflowerseed oilusing N-methyl pyrrolidone and ethyl glycol in a 9:1 w/w mixture wascarried out at 35C in a mixer settler apparatus with 12 stages. The oilcontaining 58.1 wt combined linoleic acid, was fed at a rate of 46 g/hrto the epiphase leaving stage 8, the solvent mixture was fed at about600 g/hr to stage 1, and reflux was provided by a previously enrichedsafflowerseed oil containing 80.4 wt combined linoleic acid which wasfed to stage 12 at 33 g/hr.

Equilibrium was reached in 7 hours, when the heavy phase contained 9.5wt of oil having a combined linoleic acid content of 76.8 wt while thelight phase contained 69 wt of oil of 50.6 wt combined linoleic acidcontent. The yield was 64%.

This example was repeated to obtain an enrichment greater than that ofthe reflux. For this purpose similar conditions were used, except thatan enriched safflowerseed oil reflux containing 77 wt combined linoleicacid was used and the safilowerseed oil feed was admitted at 30 g/hr tthe epiphase leaving stage 6. The heavy effluent then contained 5.6 wtof oil having a combined linoleic acid content of 79.9 wt representing alower yield of about 9%, and the light effluent contained 68 wt of oilcontaining 54 wt combined linoleic acid.

Better yields. associated with lower enrichment could be obtained byadvancing the feed point eg to stage 7.

What is claimed is:

1. Process for increasing the combined polyunsaturated fatty acidcontent of edible oils having a combined linoleic acid content of atleast 50% by weight, comprising contacting the oil with a suitablesolvent system comprising an N-substituted amide solvent selected fromthe group consisting of dimethyl formamide, N-lower alkyl pyrrolidone,and 1,6- bispyrrolidon-2-yl-,-hexane at a temperature at which twoliquid phases are formed, one consisting of a fraction of the oil richin combined linoleic acid which is dissolved in the polar solvent, andthe other a lean fraction comprising the residual oil, separating thetwo fractions and removing the polar solvent from the rich fraction torecover an oil fraction rich in combined linoleic acid.

2. Process according to claim 1 in which the polar solvent comprisesdimethylformamide.

3. Process according to claim 1 in which the polar solvent comprises anN-lower alkyl pyrrolidone.

4. Process according to claim 3 in which the polar solvent comprisesN-methyl pyrrolidone.

5. A process according to claim 1 in which the polar solvent includeseither a minor amount of water or a lower alkylene glycol containing upto 4 carbon atoms in an amount sufficient to render said polar solventimmiscible with said oil.

6. Process according to claim 1 in which the oil comprises safflowerseedoil, sunflowerseed oil or cottonseed oil.

7. Process according to claim 1 in which the oil is contacted at atemperature from 20 to 50C.

8. Process according to claim 1 in which the said solvent systemincludes a non-polar organic solvent.

9. Process according to claim 8 in which the nonpolar solvent comprisesa paraffin with from 3 to 10 carbon atoms.

10. Process according to claim 9 in which the nonpolar solvent comprisesa light petroleum with a boiling range from 96 to 98C.

11. Process according to claim 8 in which the solvent system comprisesfrom 20 to 30 parts by weight 01 polar solvent per part of non-polarsolvent.

* =l= l l l

1. A PROCESS FOR INCREASING THE COMBINED POLYUNSATURATED FATTY ACIDCONTENT OF EDIBLE OILS HAVING A COMBINED LINOLEIC ACID CONTENT OF ATLEAST 50% BY WEIGHT: COMPRISING CONTACTING THE OIL WITH A SUITABLESOLVENT SYSTEM COMPRISING AN N-SUBSITUTED AMIDE SOLVENT SELECTED FROMTHE GROUP CONSISTING OF DIMETHYL FORMAMIDE, N-LOWER ALKYL PYRROLIDONE,AND 1,6-BIS PYRROLIDON-2-YL-,-HEXANE AT A TEMPERATURE AT WHICH TWOLIQUID PHASES ARE FORMED, ONE CONSISTING OF A FRACTION OF THE OIL RICHIN COMBINED LINOLEIC ACID WHICH DISSOVED IN THE POLAR SOLVENT, AND THEOTHER A LEAN FRACTION COMPRISING THE RESIDUAL OIL, SEPARATING THE TWOFRACTIONS AND REMOVING THE POLAR SOLVENT FROM THE RICH FRACTION TORECOVER AN OIL FRACTION RICH IN COMBINED LINOLEIC ACID.
 2. Processaccording to claim 1 in which the polar solvent comprisesdimethylformamide.
 3. Process according to claim 1 in which the polarsolvent comprises an N-lower alkyl pyrrolidone.
 4. Process according toclaim 3 in which the polar solvent comprises N-methyl pyrrolidone.
 5. Aprocess according to claim 1 in which the polar solvent includes eithera minor amount of water or a lower alkylene glycol containing up to 4carbon atoms in an amount sufficient to render said polar solventimmiscible with said oil.
 6. Process according to claim 1 in which theoil comprises safflowerseed oil, sunflowerseed oil or cottonseed oil. 7.Process according to claim 1 in which the oil is contacted at atemperature from -20* to 50* C.
 8. Process according to claim 1 in whichthe said solvent system includes a non-polar organic solvent.
 9. Processaccording to claim 8 in which the non-polar solvent comprises a paraffinwith from 3 to 10 carbon atoms.
 10. Process according to claim 9 inwhich the non-polar solvent comprises a light petroleum with a 95%boiling range from 96* to 98* C.
 11. Process according to claim 8 inwhich the solvent system comprises from 20 to 30 parts by weight ofpolar solvent per part of non-polar solvent.